Cyclic elasto-plasticity behavior and fatigue crack initiation lives of low carbon steels and their simulated HAZ.

Abstract

Fatigue is one of the major causes of structural failure. In particular, the crack initiation and propagation are usually located in correspondence of the welded parts of a structure. Therefore, the correct evaluation and prediction of the fatigue life of welded components is a crucial aspect to avoid unexpected failure and to improve the design and durability of structural parts. The present study focuses on the cyclic stress-strain behavior in the weld heat-affected zone (HAZ), where mostly fatigue cracks are found. In order to investigate the cyclic plasticity behavior of HAZ including cyclic hardening and softening together, experimental and numerical campaigns are carried out. The experimental part of this study deals with the fatigue experiments conducted on test specimens that have undergone the same temperature history to which the heat-affected zone of a weld is exposed (hereafter, simulated HAZ) and the softening and hardening response of base metal, CGHAZ and FGHAZ are observed. Numerical investigations aim to reproduce the cyclic stress–strain behavior simulating the nonlinear material behavior utilizing an elasto-plasticity model called the Fatigue SS Model (hereafter, FSS model). The main feature of the FSS model is the ability to describe the cyclic softening behavior within a macroscopically elastic stress state. The cyclic stress-strain behavior predicted by numerical simulation showed good agreement with the experimental result. Finally, fatigue crack initiation life criteria of SM490A is proposed based on experimental result.